Known systems for automatically controlling the interior temperature of a motor vehicle typically include a blower fan driven by a variable-speed motor for directing air into the passenger compartment. On its way to the passenger compartment, the thus-directed air passes first through the evaporator coil of a refrigeration system (the AC coil) and then either through a heater core or an air bypass, as selected by a variable-position "air mix door" or other suitable air-blending/diverting mechanism. Such known systems also typically include a first temperature sensor for sensing the "ambient" temperature outside of the vehicle; and a second temperature sensor for sensing the actual temperature within the interior of the vehicle, i.e., at a given location within the vehicle's passenger compartment. A control unit, which includes a control panel through which a vehicle passenger may select a desired interior temperature, controls the speed at which the blower motor is operated, the relative position of the air mix door, the operation of the refrigeration system's compressor and, possibly, the operation of a heater valve regulating the flow of engine cooling fluid through the heater core, whereby the relative quantity and temperature of the directed air is controlled with a view to obtaining the desired interior temperature within a prescribed time period.
Significantly, in such known systems, when providing such automatic climate control, the control unit will typically utilize a "base" fan operating speed, either as a preselected constant or, preferably, as a function of ambient (outside) temperature alone (this, due to the fact that the ability to maintain a relatively even temperature throughout the interior of the passenger compartment is most directly impacted by ambient temperature). The control unit will typically further employ a "proportional control" algorithm responsive to the difference between the desired internal temperature and the actual interior temperature both to provide a relative percent increase in fan speed above the base fan speed (thereby arriving at a first augmented fan speed) and to control the relative position of the air mix door.
Often, prior art systems further include a sunload sensor which generates an output representative of the sun's radiant heat transfer into the vehicle's passenger compartment. In such systems, the control unit will typically employ a second proportional control algorithm responsive to the output of the sunload sensor to generate another relative percent increase in fan speed above the base fan speed due to sunload (thereby arriving at a second augmented fan speed).
Apart from maintaining the interior temperature of the vehicle at or near the desired temperature as selected by the passenger, an automatic climate control system and operating method will ideally achieve the desired interior temperature in the same manner that a passenger might otherwise himself adjust a manually-operated climate control system. Unfortunately, in known systems, its control unit unvaryingly responds to the sensed ambient temperature-interior temperature difference and/or sunload so as only to augment the base fan speed. In this manner, such systems produce a response which is often different from that which a passenger might manually choose. Specifically, a passenger will manually seek to minimize fan noise and directed airflow when attempting to arrive at the desired interior temperature, factoring in, for example, the warming effects of a relatively higher/lower ambient temperature and sunload on the vehicle's interior temperature.